This invention relates to improved gas seals, and more particularly to a dual gas seal structure and arrangement which provides for containment and utilization of gas leakage across two opposed flanges of a pressure vessel structure.
In some pressure vessel applications, a gasket or seal is employed together with a flange connection to prevent a gas such as air from escaping through flange joints. For various technical reasons, some flange joints are employed which are not capable of totally sealing an air leak and some quantity of escaping air is acceptable, particularly where the amount of escaping air does not deleteriously affect the overall system of which the air is a part.
Hot gas turbine generators ordinarily utilize an air compressor having a cylindrical casing enclosing a cylindrical bladed rotor therein. Air at atmospheric pressure is ducted into the compressor at one open end of the cylinder to be compressed by the rotating blades of the rotor interengaging with blades in the casing. Air at elevated pressure is taken from the opposite end of the casing to be directed to combustion and exhaust system regions of the gas turbine apparatus which operate at a lower pressure. The compressor casing as well as intermediate parts of the casing between the compressor and the combustion system usually comprise a multipart arrangement of component sections suitably bolted together with appropriate flanges. Unfortunately it has been found that excess air leakage may occur through the usual flat metal on metal engaging surface of the flanges of the multipart assembly, for example, because of thermal distortion of the flanges. Air leakage becomes an increasing problem where the casing structure includes curved and angled parts. It is difficult for the otherwise desirable machined surface flanges to maintain desired air sealing characteristics when the casing includes sections which are curved or at an angle to each other and the flanges are angled accordingly. For example, a flange may be utilized to seal to a horizontal as well as to a vertical surface and may utilize a single right angle flange to do so. The use of a gasket seal between the flanges is not only a deterrent to the more desirable metal to metal surface contact of the flanges, but also becomes a problem where the gasket seal might only be used where most air leakage occurs and therefore becomes an obstruction in the overall coextensive contact of the flange surfaces.